While I've only played about 4 hours of Onimusha 2, I have found it to be an excellent sequel to the already great Onimusha: Warlords from last year.
Why? Well, it seems like this is going to be a much longer game than the first, which only took me about 6 hours total to complete. As well, there are now 4 additional characters that will help out the hero, Jubei.
These characters can also be controlled at times during the game. There is also an engrossing minigame of sorts that consists of finding 'gifts' while exploring the world and trading gifts with a specific character for various doodads that enhance Jubei or that you can trade with another of the heroes.
The gameplay is pretty much the same as that in Onimusha, which was fast and furious sword action. There are also lots of magical spells to cast and the invincible 'Onimusha' form that you can change into for a limited time.
Graphically, the game itself is gorgeous, with very nice pre-rendered backgrounds and exquisite 3D characters. The CG movies are almost Square quality.
I think the nicest thing about Onimusha 2 is the fact that you will do some wandering around in a peaceful town, interacting with the citizens while taking a break from monster slaying. This makes the world seem a little more 'real' as you're not just stuck in a haunted castle with your best friend the ninja for company. The story also looks like it will make a little more sense than the original, which had villians and minor characters popping up and doing things for no apparent reason. The actions of the monsters and characters in the sequel are a little more logical.
Overall, I give it a 9. It's a lot of fun, improves on the original in almost every way and looks marvelous. If they'd included a japanese audio track as an option (rather than the mediocre english dub) I'd be tempted to give it a 10 for sheer fun.